The trend in regulation globally is for reduced bandwidth available for wireless microphones. Some countries are further ahead of others but a user should expect that there will be less bandwidth in general. For example, on Mar. 16th, 2010, the U.S. FCC published its Broadband Plan. In this plan they announced their intention to reclaim 120 MHz of the broadcast band for use in broadband access across the country.
The trend for demand is just the opposite. Large venues and installations would like to use more and more microphones simultaneously. In US cities, the recent restriction on bandwidth makes it difficult for venues to use the same number of simultaneous channels as they had in the past.
The allowed spectrum for wireless microphones in most areas of the world overlaps with the broadcast TV spectrum. Wireless microphones must be used, per regulations, in open spectrum between the channels used for TV broadcast. Depending on the region of operation, the size of the broadcast channels is either 6 MHz or 8 MHz. In Japan the spectrum available for wireless microphones is reserved outside of the TV broadcast band. There are two 9 MHz bands (A Bands) and one 4 MHz Band (B Band) available.
In the current state of the art for wireless microphone systems, there are two factors which limit the number of channels which can be used within a specified bandwidth. The two factors include channel spacing and intermodulation products. Intermodulation products may be avoided by limiting the frequencies available in a channel plan to those which are not equal to, or close to an intermodulation product of the other frequencies in the channel plan.
The prior art has avoided these difficulties by increasing the channel spacing to avoid these problems. Accordingly, a need exists for more efficient frequency use among wireless microphones.